Digestive System
Function: taking in food, breaking down food, absorbing nutrients, eliminating wastes (feces)
*Necessary because animals are heterotrophs!
Ways of Taking in Food:
*Filter feeding – collect small organisms from surrounding water
~Porifera, Mollusca (clams)
*Absorptive feeding – absorb nutrients directly through body wall
~Platyhelminthes (tapeworm)
*Ingestive feeding – use mouth to ingest food
~Cnidaria, Platyhelminthes, Nematoda, Annelida, Mollusca (snail, squid), Arthropoda,
Echinodermata, Chordata
Types Ingestive Digestive Systems:
*one-way – one opening that serves as a mouth and an anus
~Cnidaria, Platyhelminthes
*two-way (tube-within-a-tube) – two openings, a mouth and an anus
~more efficient
~Nematoda, Annelida, Mollusca, Arthropoda, Echinodermata, Chordata
Places Food is Digested:
*intracellular – food is taken into cells by phagocytosis
~Porifera, Cnidaria
*extracellular – in lumen of digestive system
~Platyhelminthes, Nematoda, Annelida, Mollusca, Arthropoda, Echinodermata, Chordata
Organs of Digestion (Chordata)
*mouth – take in food
*esophagus – transport food to stomach
*stomach – mechanical digestion
*small intestine – chemical digestion, some absorption
*large intestine – absorption, formation of feces
*rectum – removal of feces
*digestive glands – create and secrete digestives enzymes that break down food
Interactions with Other Body Systems:
*circulatory system transports nutrients to cells in the rest of your body
*circulatory system brings hormones to digestive system to speed up or slow down digestive
rate
*works with excretory system in removing waste in some species